Mechanical transmissions containing either several discrete gear ratios or continuously variable mechanisms are necessary whenever it is desirable to operate a rotating power source at certain preferred angular velocities. Transmissions are utilized for a wide variety of applications, including use in machine shop equipment, construction equipment, other types of personal and public transportation, and product handling equipment such as conveyor lines. This need is especially common in the automotive industry because internal combustion engines produce very different levels of torque and power across their operating ranges. These should not, for purposes of this application, be viewed as the only uses for the hereinafter described invention. It can be applied in any situation where it is desirable to vary the angular velocity of a rotating shaft.
Most mechanical transmissions contain a set of discrete gear ratios. This fixed number of ratios often results in an inability to continually operate the power source at its optimal setting. If a continuously variable transmission is used, however, the power source can be operated at its desired operational setting and the transmission's nominal ratio can be varied to change the angular velocity of the power output shaft as necessary.
A transmission which performs in this manner is ideally suited for use with a power source which operates at preferred, fixed angular velocities. Such a power source, commonly referred to as a CVO (for "Constant Velocity Output"), often contains a massive flywheel which is spun and preferably maintained at a constant rate. The great angular momentum of these flywheels makes altering their speed a prohibitively slow process. When coupled to a continuously variable transmission the flywheel can be driven at a constant rate, while the transmission's nominal ratio can be changed to vary the vehicle's speed as desired.
Current terminology in the art regards an infinitely variable transmission as one whose output ratio can be varied from 1:0 to some final ratio x:1, where x is some value greater than zero. Thus, at its lowest ratio, the power source of an infinitely variable transmission can rotate without driving the output shaft. Continuously variable transmissions, in contrast, can only be operated between two limiting ratios, an initial ratio y:1, where y is a value greater than zero and a final ratio z:1, where z is some value less than y.
Both infinitely and continuously variable transmissions can be adjusted so that the nominal ratio varies smoothly and without discrete, quantifiable changes between the initial and final ratios. Since the present invention can be utilized to construct a transmission having an initial ratio of 1:0, it is a true infinitely variable transmission.
There are currently two principal types of infinitely/continuously variable transmissions. The first type depends solely on friction to transmit its power. This type of transmission can be further classified into two sub-categories. One sub-category, commonly termed "pulley transmissions", uses a flexible belt to transfer power between two pulleys whose effective diameters can be varied. As the pulleys' diameters are altered the effective transmission ratio varies. In the other sub-category, power is transferred through contact with a body of continuously varying shape. The typical shape is that of a cone or hyperboloid rotating about its center line. The nominal ratio will depend on where the continuously varying shape is contacted by the pickup shaft, since its effective diameter changes along its length.
The second principal type of variable transmission transfers power using direct engaging mechanical contact, typically through gears. Such transmissions can be distinguished from the aforementioned "friction drives" because mechanical engagement transmissions do not transfer power solely by way of the shearing force developed as a result of the contact force exerted between two moving surfaces. (When two surfaces press against one another the resulting force vector can be resolved into two components. The normal component is that perpendicular to the contact plane of the two surfaces. The tangential, or shear component is the force exerted parallel to the contact plane of the surfaces.) In these mechanical drives, part, if not all, of the power is transferred via this shear force component. The present invention is of this second type of transmission.
All existing designs for continuously and infinitely variable transmissions have a number of shortcomings. Each of the types previously mentioned has its own peculiar problems, caused, inter alia, by the manner in which the tranmission's ratio is altered.
Both types of friction drives, i.e. pulley and variable diameter driving bodies, rely on friction to transfer power. The easiest way to decrease slippage, and thus power loss, is by increasing the contact forces between the parts transferring power. As this contact force increases, however, various problems may arise. Among these problems are structural fatigue and deformation. The touching parts may even begin to wear, necessitating replacement of the belt, pulley or rotating body.
Variable transmissions using mechanisms other than pure friction, such as gears, to transfer power typically contain a substantial number of parts. See, for example, U.S. Pat. No. 4,184,388 (Sfredda). The Sfredda transmission, like the present one, is a mechanical transmission of the second type. Sfredda discloses an infinitely variable transmission utilizing a planetary gear system requiring a large number of parts to effect variability. The instant invention is readily distinguished from this and other transmission art because of its drastic simplification and reduction of parts. In fact, prior art teaches away from such simple mechanisms used in the present invention. This simplification is a primary advantage of the present invention.